Detailed photocurrent spectroscopy of the semiconducting group VIB transition metal dichalcogenides

Kam, K. K.; Parkinson, B. A.

doi:10.1021/j100393a010

Cited by 861 publications

(633 citation statements)

References 5 publications

Supporting

Mentioning

585

Contrasting

Order By: Relevance

“…Many TMDCs have band structures that are similar in their general features, as shown by first principles and tight-binding approximations 25,[80][81][82][83][84][85] and measured using a variety of spectroscopic tools 31,32,[86][87][88][89] . In general, MoX 2 and WX 2 compounds are semiconducting whereas NbX 2 and TaX 2 are metallic 25,[80][81][82][83][84] .…”

Section: Electronic Structurementioning

confidence: 99%

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

et al. 2012

View full text Add to dashboard Cite

699M any two-dimensional (2D) materials exist in bulk form as stacks of strongly bonded layers with weak interlayer attraction, allowing exfoliation into individual, atomically thin layers 1 . The form receiving the most attention today is graphene, the monolayer counterpart of graphite. The electronic band structure of graphene has a linear dispersion near the K point, and charge carriers can be described as massless Dirac fermions, providing scientists with an abundance of new physics 2,3 . Graphene is a unique example of an extremely thin electrical and thermal conductor 4 , with high carrier mobility 5 , and surprising molecular barrier properties 6,7 .Many other 2D materials are known, such as the TMDCs 8,9 , transition metal oxides including titania-and perovskite-based oxides 10,11 , and graphene analogues such as boron nitride (BN) 12,13 . In particular, TMDCs show a wide range of electronic, optical, mechanical, chemical and thermal properties that have been studied by researchers for decades 9,14,15 . There is at present a resurgence of scientific and engineering interest in TMDCs in their atomically thin 2D forms because of recent advances in sample preparation, optical detection, transfer and manipulation of 2D materials, and physical understanding of 2D materials learned from graphene.The 2D exfoliated versions of TMDCs offer properties that are complementary to yet distinct from those in graphene. Graphene displays an exceptionally high carrier mobility exceeding 10 6 cm 2 V -1 s -1 at 2 K (ref. 16) and exceeding 10 5 cm 2 V -1 s -1 at room temperature for devices encapsulated in BN dielectric layers 5 ; because pristine graphene lacks a bandgap, however, fieldeffect transistors (FETs) made from graphene cannot be effectively switched off and have low on/off switching ratios. Bandgaps can be engineered in graphene using nanostructuring [17][18][19] , chemical functionalization 20 and applying a high electric field to bilayer graphene 21 , but these methods add complexity and diminish mobility. In contrast, several 2D TMDCs possess sizable bandgaps around 1-2 eV (refs 9,14), promising interesting new FET and optoelectronic devices.TMDCs are a class of materials with the formula MX 2 , where M is a transition metal element from group IV (Ti, Zr, Hf and so on), group V (for instance V, Nb or Ta) or group VI (Mo, W and so on), and X is a chalcogen (S, Se or Te). These materials form layered structures of the form X-M-X, with the chalcogen atoms in two hexagonal planes separated by a plane of metal atoms, as shown in Fig. 1a. Adjacent layers are weakly held together to form the bulk crystal in a variety of polytypes, which vary in stacking orders and metal atom coordination, as shown in Fig. 1e. The overall symmetry of TMDCs is hexagonal or rhombohedral, and the metal atoms have octahedral or trigonal prismatic coordination. The electronic properties of TMDCs range from metallic to semiconducting, as summarized in Table 1. There are also TMDCs that exhibit exotic behaviours such as charge density waves ...

show abstract

Section: Electronic Structurementioning

confidence: 99%

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

et al. 2012

View full text Add to dashboard Cite

show abstract

“…Single-layer MoS 2 (extracted from naturally occurring 2-H-phase material) has a direct electronic band gap ~1.8 eV [1,2] while bulk 2-H phase MoS 2 exhibits a lower indirect band gap ~ 1.3eV [3]. This semiconducting nature has been exploited to create MoS 2 field effect transistors (FETs) [4] with high on-off ratio and ultrasensitive photodetectors [5], amongst other optoelectronic and photonic [6,7] devices.…”

Section: Introductionmentioning

confidence: 99%

Identifying different stacking sequences in few-layer CVD-grownMoS2by low-energy atomic-resolution scanning transmission electron microscopy

et al. 2016

View full text Add to dashboard Cite

ABSTRACT:Atomically thin MoS 2 grown by chemical vapor deposition (CVD) is a promising candidate for the next-generation electronics due to inherent CVD scalability and controllability. However, it is well-known that the stacking sequence in few-layer MoS 2 can significantly impact the electrical and optical properties. Herein we report different intrinsic stacking sequences in CVD grown few-layer MoS 2 obtained by atomic-resolution annular-dark-field imaging in an aberration-corrected scanning transmission electron microscope operated at 50 keV. Tri-layer MoS 2 displays a new stacking sequence distinct from the commonly observed 2H and 3R phases of MoS 2 . Density functional theory is used to examine the stability of different stacking sequences, and the findings are consistent with our experimental observations.

show abstract

“…The energy difference of 0.2eV has been attributed to the degeneracy breaking of the valence band due to spin-orbit coupling [4,7,8,22]. As compared to bulk MoS 2 , Fig.1b, 1L-MoS 2 does not have a peak at 1.4eV [3,4], associated with the indirect band gap [12]. In addition 1L-MoS 2 exhibits a stronger PL intensity compared to bulk MoS 2 [3, 4] due to the direct band gap.…”

mentioning

confidence: 99%

“…This property has been exploited in lubrication technology [10] and, more recently, has lead to the isolation of 1L-MoS 2 [2][3][4]11]. While bulk MoS 2 is a semiconductor with an indirect band gap of 1.3 eV [12], 1L-MoS 2 has a direct band gap of 1.8 eV [3,4]. The absence of interlayer coupling of electronic states at the Γ point of the Brillouin zone in 1L-MoS 2 [4,13] results in strong absorption and PL bands at∼1.8eV (680nm) [3,4].…”

mentioning

confidence: 99%

Electroluminescence in Single Layer MoS₂

et al. 2013

View full text Add to dashboard Cite

We detect electroluminescence in single layer molybdenum disulphide (MoS2) field-effect transistors built on transparent glass substrates. By comparing absorption, photoluminescence, and electroluminescence of the same MoS2 layer, we find that they all involve the same excited state at 1.8eV. The electroluminescence has pronounced threshold behavior and is localized at the contacts. The results show that single layer MoS2, a direct band gap semiconductor, is promising for novel optoelectronic devices, such as 2-dimensional light detectors and emitters. Here, we report electrically excited luminescence in 1L-MoS 2 FETs, and study the underlying emission mechanism. We find that the electroluminescence occurs via hot carriers and is localized in the contacts region. The observed photoluminescence and electroluminescence arise from the same excited state at 1.8eV. Molybdenum disulphide (MoS1L-MoS 2 crystals are produced by micromechanical cleavage of bulk MoS 2 (Structure Probe Inc.-SPI, Natural Molybdenite) on 100nm SiO 2 . As for the case of graphene [20], interference allows visibility and counting the number of layers, Fig.1a. Due to the different dielectric properties, an optimum thickness of 100nm SiO 2 is well suited for MoS 2 [21]. The presence of monolayers is then confirmed by performing PL measurements, Fig.1b. The PL spectrum of 1L-MoS 2 exhibits two bands at 2eV and 1.8eV (Fig.1b) associated with excitonic transitions at the K point of the Brillouin zone[4]. The energy difference of 0.2eV has been attributed to the degeneracy breaking of the valence band due to spin-orbit coupling [4,7,8,22]. As compared to bulk MoS 2 , Fig.1b, 1L-MoS 2 does not have a peak at 1.4eV [3,4], associated with the indirect band gap [12]. In addition 1L-MoS 2 exhibits a stronger PL intensity compared to bulk MoS 2 [3, 4] due to the direct band gap. Another evidence for 1L-MoS 2 comes from the analysis of the Raman spectrum, Fig.1d. The peak at∼385cm −1 corresponds to the in plane (E 1 2g ) mode [23], while that at ∼404 cm −1 is attributed to the out of plane (A 1g ) mode [23]. The E 1 2g mode softens and A 1g mode stiffens with increasing layer thickness[23], similar to what happens for other layered materials, where the bond distance changes with number of layers [24]. The frequency difference between these two modes can be used as a signature of 1L-MoS 2 [23].1L-MoS 2 flakes are then transferred onto glass substrates by using a poly(methyl methacrylate) (PMMA) based transfer technique, similar to that previously used to transfer graphene onto optical fibre cores [25]. This process involves spin coating two layers of 495K PMMA and one layer of 950K PMMA on the substrate where flakes are deposited. The samples are subsequently immersed in de-ionized (DI) water at 90 • C for 1h, resulting in the detachment of the polymer film, due to the intercalation of water at the polymer-SiO 2 interface. MoS 2 flakes stick to the PMMA, and can thus be removed from the original substrate and mechanically transferred onto glass substrates [2...

show abstract

Detailed photocurrent spectroscopy of the semiconducting group VIB transition metal dichalcogenides

Cited by 861 publications

References 5 publications

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

Identifying different stacking sequences in few-layer CVD-grownMoS2by low-energy atomic-resolution scanning transmission electron microscopy

Electroluminescence in Single Layer MoS₂

Contact Info

Product

Resources

About

Detailed photocurrent spectroscopy of the semiconducting group VIB transition metal dichalcogenides

Cited by 861 publications

References 5 publications

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

Electronics and optoelectronics of two-dimensional transition metal dichalcogenides

Identifying different stacking sequences in few-layer CVD-grownMoS2by low-energy atomic-resolution scanning transmission electron microscopy

Electroluminescence in Single Layer MoS2

Contact Info

Product

Resources

About

Electroluminescence in Single Layer MoS₂